The prior patent literature includes U.S. Pat. No. 4,964,936 to Ferro shows open cells of honeycomb core filled with polyimide foam in contrast to the present insulation blanket which incorporates solid panels of polyimide sandwiched in a stacked relationship with layers of fiber glass.
U.S. Pat. No. 5,169,700 to Meier, et al, shows a single layer or multilayer blanket of fibrous material, the fibrous material specified as fiber glass. Each single layer is bonded to an air permeable face sheet. The multilayer blankets are edge-stitched or contained in a heat sealable film. The density of the blanket ranges between 0.2 and 1.5 pounds per cubic foot. In contrast, the present invention utilizes multilayer stackup wherein a core layer of stiffer polyimide foam is sandwiched between layers of fiber glass blankets. The present invention, utilizing the aforementioned combination of materials which possesses different impedances and densities, provides optimum noise transmission loss characteristics in contrast to Meier, et al, based on materials possessing a single density within the stated range.
Various problems have been associated with insulation blankets used in aircraft interiors. Typical problems encountered are as follows:
(a) Under current fabrication methods, fiber glass blankets are covered with mylar and stitched to retain shape. Extensive sewing and/or attachment pins are required to keep the current insulation batting from slumping inside the bagging or face sheet. PA1 (b) Sewing face sheets to batting insulation and taping over the sewn areas are required. Taping is necessary to prevent moisture absorption by capillary action, because moisture absorption goes into the blanket through stitching. PA1 (c) All peripheral and internal cutouts require complex stitching which must be sealed to stop moisture absorption and accumulation thereby adding cost and weight. PA1 (d) Moisture is entrained causing increased insulation weight and water accumulation which causes acoustic and thermal performance degradation. PA1 (e) Maintenance cost to airline customers is high due to the current insulation removal and re-installation practice. PA1 (f) Insulation blankets are typically the single heaviest payloads item, because they cover the entire surface area of the fuselage. Therefore, a small reduction in unit weight achieves very large total weight reduction and improved airplane performance.